Compound Semiconductor Science and Technology Thrust
The Physical, Chemical, and Nano Sciences Center's vision for Compound Semiconductors is to develop the science of compound semiconductors that will enable us to invent integrated nano-technologies for the microsystems of the future. We will achieve this by advancing the frontiers of semiconductor research in areas such as quantum phenomena, defect physics, materials and device modeling, heteroepitaxy, and by discovering new materials and inventing new device structures with novel properties.
The focus of the compound semiconductor science and technology thrust is to understand and exploit compound semiconductor materials and devices for national security applications. We are developing the fundamental physics and chemistry foundations to advance the state-of-the-art compound semiconductor optoelectronic materials and devices. Our approach is based on a focused effort including materials synthesis, characterization, theoretical modeling, device design and processing. Our research portfolio encompasses quantum phenomena, defect physics, materials and device modeling, heteroepitaxy, semiconductor nanostructures, and developing new materials and device structures with novel properties.
Our efforts are focused on the following areas of semiconductor research:
Solid-State Lighting
In the future, solid-state electro-optical devices based on new materials are likely to become capable of producing white light for general building illumination at significantly higher efficiencies than existing conventional light sources, with potential energy cost savings of up to $100 B per year. DOE Office of Building Technologies is presently sponsoring a joint industry/national lab/university technology roadmapping project on developing high efficiency LEDs and laser diodes for this purpose. If successful, the initiative would fund a multi-year research and development effort, the Solid-State Lighting Initiative. Sandia is currently coordinating the roadmapping effort with the Optoelectronics Industry Development Association under sponsorship of the DOE, and will likely play a significant role in the Initiative, for example, in establishing the fundamental science and technology base needed in order for this vision of ultra-efficient solid-state illumination to become a reality. Research in this area includes improvements in nitride and phosphide based growth chemistry, reactor design, and light emitting devices including LEDs and VCSELS in the red, green, blue, and ultraviolet wavelength ranges.
Semiconductor Synthesis
We are also responsible for research, development, and application of chemical science to materials technologies critical to Sandia's missions. Our work currently emphasizes the science and engineering of Metal Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), and nanostructure synthesis and characterization. We are also involved in the synthesis and characterization of other novel materials such as carbon nanotubes, nanoporous carbon, high temperature superconductors, and various metal and semiconductor thin films using techniques such as pulsed laser deposition and thermal chemical vapor deposition.
MOCVD is a technology for producing inorganic thin films. MOCVD is a crucial step in the fabrication of GaN- and GaAs-based microelectronic and optoelectronic devices and nanostructures, as well as being used for depositing protective coatings. We advance the state-of-the-art in MOCVD and related technologies through an interdisciplinary approach which includes a wide range of experimental and theoretical techniques and an extensive network of partners inside and outside of Sandia. Using MOCVD we are investigating novel GaN-based structures for the development of high efficiency solid-state lighting and ultraviolet light emitters, quantum dot structures for infrared technologies, and improved in-situ diagnostic instrumentation.
MBE is a ultrahigh vacuum technique for producing inorganic thin films starting from elemental sources. It is predominantly used for the production of multilayered compound semiconductor epitaxial structures. Using MBE, materials can be produced with both high purity and careful control of compositions and thicknesses. We are using this technique to produce GaAs-based structures to study quantum transport phenomena as well as electronic devices based on interband electronic transitions. This work uses a wide range of other experimental and theoretical techniques both at Sandia and at universities throughout the country.
We also develop synthesis and processing methods for producing chemically pure, highly crystalline metal and semiconductor nanoclusters with controlled sizes and interfaces. A significant aspect of this synthetic effort involves the development of new analytical methods to rapidly provide quantitative information concerning cluster size, size dispersion, interface chemistry, chemical composition, and optical/electronic behavior of the nanocrystals. Similar chemical analysis techniques are also used for the detailed investigation of the physical properties of nanocluster composites germane to energy applications such as catalysis, photocatalysis, and light emission.
Nanotechnology
We also have research programs that are directed at understanding the physics of small dimensions. We apply this knowledge to develop new nanoscale structures and concepts for nanoelectronic, photonic, micro-optical sensing, micromechanical, and other applications. Since microscopic things seldom behave like macroscopic devices, we must develop atomic level understanding of our microdevices. We have particularly strong capabilities in the kinetics and microstructure of thin film synthesis, processing and aging, and in the behavior of nanophotonic and nanoelectronic structures.
Defect Physics and Quantum Phenomena
Defects and impurities in semiconductor materials limit their performance by degrading the electrical and optical properties of the materials. A fundamental understanding of the roles of defects, impurities and dopants and their interactions with each other helps us understand observed electrical and optical behaviors and provide pathways for improved performance. The large bandgaps and bonding characteristics of compound semiconductors means that the extensive body of research done on elemental semiconductors and low bandgap compounds is of little relevance in helping us understand atomic processes in these materials. We use ab-initio density-functional theory (DFT) calculations to understand the atomic processes and configurations in these materials, utilizing the key capabilities of the Sandia massively parallel computing environment. These studies provide information on atomic configurations, charge states, formation energies, diffusion barriers, trapping reactions, dopant/impurity-defect reactions and effects of irradiation. We are particularly interested in the atomic processes involving hydrogen, native defects, impurities and dislocations, including their role in the detrimental compensation of p-type dopants.
Compound Semiconductor Research Laboratory
Much of our research takes place in and around the Compound Semiconductor Research Laboratory which includes a 6500-square foot, Class 100 cleanroom fabrication facility. This facility provides capabilities for application-driven research and development of microsystems technologies. The Microsystems and Engineering Sciences Applications West Operations organization is responsible for maintaining laboratory flexibility (for research and development activities) while improving the quality and implementation of processes to meet increasingly formalized deliverable requirements of our customers (prototyping and deliverables activities). The goal of the organization is to improve the efficiency of operations, increase the professionalism of implementation, and ensure the delivery of quality product to our customers. This is being accomplished through the adoption and monitoring of process performance metrics, the introduction of preventative maintenance routines, and the development of an expert process engineering and equipment maintenance staff. In this facility, we emphasize innovative science in compound semiconductor materials and device development. In partnership with our DOE, government, and industrial partners, we provide innovative technical solutions to important national security missions and industrial needs. Our technological strength is rooted in decades of fundamental research into the underlying science supporting state of the art compound semiconductor systems. We have the technical depth to work across the spectrum from the deep UV to the far IR and THz.
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Density-Functional Theory (DFT)